In paint spray booths as now operated there is continuous air exhaust through an exhaust duct, even when no painting is being done. When paint spraying is resumed it is necessary to supply heated make-up air. This necessarily results in a very significant waste of energy.
The prior art does disclose a power operated damper in a ventilation duct which is automatically opened and closed in response to the starting and stopping of a wood working machine requiring a ventilation system to exhaust undesirable byproducts. See U.S. Pat. No. 3,616,745 issued to J. C. Russell, Sr. on Nov. 2, 1971. Also, U.S. Pat. No. 3,596,671 issued to Scharfenberger discloses a control mechanism operative to stop the operation of electrostatic operating equipment in response to the failure or the reduced efficiency of ventilating apparatus for a coating booth. However, this is the reverse of the exhaust duct control system disclosed herein.
It is also known to automatically actuate a fire damper in a ventilation duct to a closed position by a spring loaded arrangement responsive to the melting of a fusible link. See U.S. Pat. No. 3,283,691 issued on Nov. 8, 1966 to W. Reiter.
The exhaust system set forth herein is operable in a manner not disclosed by the known prior art to automatically close a damper in an exhaust duct from a paint spray booth in response to the cessation of paint spraying operations and to hold the damper closed against differentials in air pressure which may develop across the face of the damper; and this feature is combined with a fire prevention mechanism which operates to close the damper in the event of fire through a fusible link actuated mechanism coupled to the damper drive shaft.